Degenerative plate circuit detector



Oct. 8, 1940. s. HUNT DEGENERATIVE PLATE cmcun: DETECTOR Filed Sept. 28, 19:8

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fi| I 70 A. E AMPLIFIER INVENTOR. se MOUR HUNT Patented Oct. 8, 1940 UNITED STATES ICE DEGENERAT'IVE PLATE CIRCUIT DETECTOR Application September 28, 1938, Serial No. 232,075

6 Claims.

My present invention relates to detector circuits, and more particularly to degenerative plate circuit detectors capable of substantially amplifying the audio voltage output thereof.

One of the main objects of this invention is to provide a detector of the infinite impedance type which includes an electronic section having a negative mutual conductance characteristic which functions to amplify the audio output of the detector.

Another important object is to provide in a biased plate circuit detector of the degenerative type a negative mutual conductance section which acts to increase the current flow through the detector plate circuit when the input signal amplitude increases.

Still other objects of my present invention are to improve generally the efiiciency of degenerative plate circuit detectors, and more especially to provide a detector of the latter type which is not only reliable in operation but is economically manufactured and assembled.

The novel features which I believe to be characteristic of my invention are set forth in par- 25 ticularity in the appended claims; the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically a circuit organization whereby my invention may be carried into effect.

Referring now to the accompanying drawing, there is shown used as the detector an electron discharge tube of the GA? or 6A8 type. This type of tube comprises a cathode I and a plate 2; betwee-n these electrodes are positioned electrodes 3, l, 5, t, l in succession in the electron stream. Plate 2 is left free, whereas cathode i is connected to ground through a resistor 8. The high potential side of the signal input circuit 9 is connected to the signal input electrode 3. The low potential side of circuit 9 is grounded; condenser connects the ground end of input circuit 9 to the cathode end of resistor 8. Condenser iii has a low impedance for carrier frequency currents, but has a high impedance to audio frequency components. Hence, there is developed across resister 3 both direct current voltage and audio frequency voltage components. These components are impressed on the input electrode 3.

The primary circuit H maybe fixedly tuned to the I. F. (intermediate frequency) value of a superheterodyne receiver; the same being true of secondary circuit 9. Since those skilled in the art are fully acquainted with the construction of superheterodyne receivers, it is not believed necessary to explain the construction thereof at any greater length. The output electrode for the detector circuit includes electrode 4. Preferably, this electrode is a wound grid. The latter is connected through load resistor 52 to the plus B terminal of any desired direct current source, such as the usual direct current energizing source of a radio receiver. The coupling condenser l3 transmits the audio voltage, in amplified form, to the following audio amplifier for final reproduction.

The electrodes l3t, With associated circuits, provide a degenerative plate circuit detector, or infinite impedance diode detector as it is sometimes termed. There has been disclosed. and claimed by P. A. Farnham in application Serial No. 8,664, filed March 1, 1935, such a detector. It is though sufficient for the purposes of this disclosure to make reference to the latter, and briefly state that substantially linear detection is secured in this type of detector by providing a direct current voltage across resistor 8 sufficient to bias grid 3 almost to cut-01f in the absence of signals. Further, the audio voltage across cathode resistor i5 is in degenerative phase, and tends to compensate for the non-linearity of the detection characteristic for weak signals. However, by virtue of this degenerative action the gain of the detector is less than unity. The present invention provides gain for the detector of the degenerative type.

This is accomplished by connecting electrode 6 to ground. The screen electrodes 5 and l are both connected to a source of positive potential, and I. F. by-pass condenser it connects the energizing lead to ground. As grid 3 becomes less negative due to the applied signals, more electrons ilow to the screens 5l. The flow of current causes a virtual cathode to build up between the detector plate electrode 4 and the screen electrodes. As the virtual cathode becomes more intense, the potential of grid 6 becomes more negative due to the increased voltage across resistor 8. The negative potential of grid 8 drives the electronstowards detector plate i, and, therefore, causes the plate current flow through output resistor it to increase. Hence, the audio voltage developed across the output resistor 52 is augmented by the action of the grid 6 and screen, or plate, 5'l. Actually as the signal gets stronger, the electron flow to plate 5 is increased by the joint action of grids 3 and 6. g

It may be pointed out that electrodes l5 and 6 cooperate with the virtual cathode to provide a device having negative mutual conductance. In other words, the flow of electrons towards the plate electrode 4 increases as the bias on grid 6 increases. This is the reverse of grid 3 which causes the current to plate electrode 4 to increase with decrease of negative bias thereof. There is provided, by means of the present invention, a detector whose detection characteristic is linear over a wide signal amplitude range, and whose audio voltage output is substantially amplified with respect to the same detector circuit when not employing the invention.

While I have indicated and described a system for carrying my invention into effect, it

will be apparent to one skilled in the art. that my invention is by no means limited to the particular organization shown and described, but that many modifications may be made without departing from the scope of my invention, as set forth in theappended claims.

What I claim is:

l. In :combination, in a detector tube, an electronic section having a positive mutual conductance and having a signal input circuit and an output electrode, a second electronic section having a negative mutual conductance and provided with a control electrode responsive to the space current flow of the first section, said control electrode being an electrode of said tube other than said output electrode and being spaced from said output electrode, the said output electrode being common to both sections.

2. In a tube of the type having a cathode and a positive output electrode, a signal input electrode therebetween, means for biasing the input electrode negative with respect to the cathode, a second positive electrode spaced from the output electrode and providing a virtual cathode therebetween, and a control electrode disposed adjacent the virtual cathode, and responsive to an increase in space current flow through the tube, for causing electrons to flow from the virtual cathode to said output electrode.

3. In a tube of the type having a cathode and a positive output electrode, a signal input electrode therebetween, means for biasing the input electrode negative with respect to the cathode, a second positive electrode spaced from the output electrode and providing a virtual cathode there between, and a control electrode disposed ad-' jacent the virtual cathode, and responsive to an increase in space current flow through the tube,-

for causing electrons to flow from the virtual cathode to said output electrode, an impedance in the space current path of the tube for deriving an audio voltage from impressed signals, said audio voltage being impressed on said signal input electrode in degenerative phase.

4. In a tube of the type having a cathode and a positive output electrode, a signal input elec trode therebetween, means for biasing the input electrode negative with respect to the cathode, a second positive electrode spaced from the output electrode and providing a virtual cathode therebetween, and a control electrode disposed adjacent the virtual cathode, and responsive to an increase in space current flow through the tube, for causing electrons to flow from the virtual cathode to said output electrode, an audio output circuit coupled to said output electrode, said control electrode being connected .to a point assuming an increasing negative potential with respect to said cathode.

5. In a detection network, a tube having at least a cathode, input electrode and output elec-- trode, a signal input circuit connected to the cathode and input electrode, means coupled to the output electrode for deriving an audio voltage from detected signals, means for impressing a portion of derived audio voltage between the input electrode and cathode in degenerative phase, means in said tube for attracting electrons beyond said output electrode, and additional means in said tube, responsive to space current increase, for causing said attracted electrons to flow back to said output electrode thereby to increase the magnitude of the audio voltage,

6. In a detector network, a tube having a cathode, signal grid, output grid, control grid and positive electrode arranged in the order named, a signal input circuit, an impedance connected between cathode and ground and being traversed by the space current of the tube, said' input circuit being connected between the signal grid and ground, an audio voltage load connected to the output grid, and a connection from the control grid to ground whereby an increase in space current of the tube results in an augmentation of audio voltage developed across said load.

SEYMOUR HUNT. 

